Ionization devices or ionizers generate positive and negative ions for delivery to a target area and are commonly used in a wide variety of industries to remove or minimize static charge accumulation in a work area. Ionizers are also commonly referred to as static charge neutralizers.
An example of the ionizer is an ionizing blower. An ionizing blower typically includes an ion source that generates positive ions and negative ions using the so-called “corona method.” The ionizing blower includes a fan (or a number of fans) or pressurized gas stream to blow or direct the ions towards a target area.
With the corona method, a high voltage (e.g., 5 kV-20 kV) is applied to a set of sharp points (often needle-like structures), and an intense electric field with ultra-high value of the electric strength vector gradient is established near these sharp points. The electric field accelerates free electrons to a sufficiently high energy in order to allow the free electrons to collide with molecules so as to ionize the molecules. When the voltage on one of the points is positive, positive ions are repelled into the environment and when the voltage on one of the points is negative, negative ions are repelled into the environment.
Corona ionizers may be designed to work with AC voltage or DC voltage, and the use of AC or DC voltage may provide different benefits. Other types of ion sources also exist and may be used in ionization devices. For example, ion sources may also use ionizing radiation to generate ions via the so-called alpha ionizer method.
With ionizers, it is important to monitor efficiency of neutralizing static charge and this is usually measured by discharge time (or decay time), which is the time required for an electrostatic potential of the state charge to be reduced to a given percentage (usually 10%). The decay time may be measured using the so-called CPM (Charge Plate Monitor) method in which a sensor plate is placed at a work area where the ionization is to be measured. The sensor plate is first charged to a preset voltage and then allowed to dissipate to a specified voltage while measuring the duration of the discharge. The sensor plate is typically designed as conductive plate with a fixed plate-to-earth capacitance of 20 pF and the decay time is defined as the time taken for the charge on the sensor plate to drop from 1000V to 100V.
This approach is commonly used to characterize the ionizer but may not be convenient for monitoring because it requires placing the bulky sensor plate at the work area, periodically charging it to a high voltage of 1000V and waiting from seconds to minutes until the plate discharges.
An alternate way to characterize of an ionizer is based on ionic current measurement. Ionic current may comprise a number of ions delivered per unit area to a target area, and may be affected by type and quality of the ion source as well as the strength of the fan (or fans) or gas pressure (for compressed gas ionizers) that deliver the ionized air or gas from the ionization devices. The ion current may be measured using the so-called BPM (Bias Plate Monitor) method in which the sensor plate is connected through an isolated current meter to a high voltage power supply. This technique gives a possibility to determine decay time indirectly on the basis of the ionic current value and may reduce the time of measurement. However, this technique still requires high voltage power supply and additional wiring.
It is an object of the present invention to provide an ionization monitoring device and method to address at least one of the disadvantages of the prior art and/or to provide the public with a useful choice.